scholarly journals Vibrational Spectroscopy of Homo- and Heterochiral Amino Acid Dimers: Conformational Landscapes

Molecules ◽  
2021 ◽  
Vol 27 (1) ◽  
pp. 38
Author(s):  
Haolu Wang ◽  
Matthias Heger ◽  
Mohamad H. Al-Jabiri ◽  
Yunjie Xu

The homo- and heterochiral protonated dimers of asparagine with serine and with valine were investigated using infrared multiple-photon dissociation (IRMPD) spectroscopy. Extensive quantum-chemical calculations were used in a three-tiered strategy to screen the conformational spaces of all four dimer species. The resulting binary structures were further grouped into five different types based on their intermolecular binding topologies and subunit configurations. For each dimer species, there are eight to fourteen final conformational geometries within a 10 kJ mol−1 window of the global minimum structure for each species. The comparison between the experimental IRMPD spectra and the simulated harmonic IR features allowed us to clearly identify the types of structures responsible for the observation. The monomeric subunits of the observed homo- and heterochiral dimers are compared to the corresponding protonated/neutral amino acid monomers observed experimentally in previous IRMDP/rotational spectroscopic studies. Possible chirality and kinetic influences on the experimental IRMPD spectra are discussed.

2019 ◽  
Vol 15 ◽  
pp. 1534-1544
Author(s):  
Abdulselam Adam ◽  
Saber Mehrparvar ◽  
Gebhard Haberhauer

The combination of photo-switchable units with macrocycles is a very interesting field in supramolecular chemistry. Here, we present the synthesis of a foldable container consisting of two different types of Lissoclinum macrocyclic peptides which are connected via two azobenzene units. The container is controllable by light: irradiation with UV light causes a switching process to the compact cis,cis-isomer, whereas by the use of visible light the stretched trans,trans-isomer is formed. By means of quantum chemical calculations and CD spectroscopy we could show that the trans→cis isomerization is spatially directed; that means that one of the two different macrocycles performs a definite clockwise rotation to the other, caused by irradiation with UV light. For the cis→trans isomerization counterclockwise rotations are found. Furthermore, quantum chemical calculations reveal that the energy of the cis,cis-isomer is only slightly higher than the energy of the cis,trans-isomer. This effect can be explained by the high dispersion energy in the compact cis,cis-isomer.


2020 ◽  
Vol 124 (12) ◽  
pp. 2408-2415 ◽  
Author(s):  
Åke Andersson ◽  
Mathias Poline ◽  
Meena Kodambattil ◽  
Oleksii Rebrov ◽  
Estelle Loire ◽  
...  

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